735
FXUS61 KCTP 300127
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
927 PM EDT Sat Jun 29 2024

.SYNOPSIS...
A cold front will push through central Pennsylvania on Sunday.
A large high pressure system will build into the region early
in the upcoming week, followed by a dying cold front pushing in
from the Great Lakes and stalling out over the area late next
week by the middle of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
Lingering convection is sub-severe as it traverses the Lower
Susq and northeast MD this evening. Some interesting
circulations lasted past 8PM across the area but trends in the
past 25 minutes have indicated the threat to be mostly over.
Latest model guidance indicates isold to scattered coverage of
showers and still some isold thunderstorms, mainly across the
southern third of PA, will shift east of the region after
midnight, as the lead shortwave and plume of highest pwats exit
the state. Some areas of fog are very likely given high surface
dewpoints and light winds ahead of the cold front that will be
approaching from the GLAKS and Ohio Valley overnight.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH 6 PM SUNDAY/...
Passage upstream surface cold front will bring the chance for
another round of convection Sunday. Locations most likely to see
potential strong/svr t-storms are over the southeastern part of
the CWA due to a fropa coinciding with peak heating of the late
afternoon.

Lows tonight will be very mild and in the mid 60s to mid 70s or
10 to 15 deg F above normal.

Max temps Sunday will be a few to several deg F higher than
today (Sat) in all locations.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Once the cold front clears, the door will be open for another
seasonably cool/dry airmass to invade the Commonwealth. This
will result in a less humid and comfortably dry start to July on
Monday.

A fair and cool Monday night looks likely as high pressure and
associated dry airmass build directly over PA, resulting in
efficient radiational cooling and min temps several degrees
below normal. Fair and warmer weather is expected Tuesday into
at least the first half of Wednesday, as upper level ridging
builds over the state and surface high drifts offshore.

All medium range guidance tracks a weakening shortwave well
north of PA late Wednesday into Thursday. The dying cold front
is likely to sag into the state Thursday and stall out in the
vicinity of PA through Friday. Falling heights/surging low level
moisture ahead of the front could support scattered convection
as early as Wednesday afternoon over the northwest half of PA.
However, a better chance of showers/tsra areawide will come
with the arrival of the front Thu into Friday. Early best guess
of late week rainfall based on ensemble plumes ranges from 0.25
to 0.75 inches, with the highest amounts over the N Mtns and
least in the south.

Heat and humidity should peak ahead of the front Wed-Thu.
Ensemble mean 850mb temps surging to near 20C indicate max temps
could reach the low to perhaps mid 90s in the Lower Susq Valley
Thursday, with high humidity pushing heat indices into the mid
and upper 90s. Ensemble plumes suggest slightly cooler daytime
temps late week, due to more clouds/showers. However, high pwats
in the vicinity of the stalling front should result in muggy
nights and above normal min temps the entire second half of next
week.

Models begin to diverge as we head into the weekend. Most
guidance suggests that rain chances stick around through at
least Saturday as another cold front approaches the area.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
A few more adjustments made just before I sent the 00 TAF
package. Main thing was to add in some VCSH early on, as
the airmass is supporting a few showers forming since
about an hour ago.

Earlier discussion below.

Adjusted TAFS several times this afternoon and early this
evening, as line of storms that formed over the mountains
earlier this afternoon have been moving along at a rather fast
pace. Still concern that the far southeast activity may slow
some, given the southeast flow and very high dewpoints in place
now.

Main change to the 00Z TAF package was to back off on
showers overnight, and put showers in toward Sunday morning,
given location of main cold front and upper level forcing.

Still expect conditions to improve later Sunday, as the winds
shift to the northwest and much less humid air moves into the
area from northwest to southeast.

Monday and Tuesday look dry at this point with a dry airmass
and VFR conditions, as high pressure builds into the area.
A bit breezy on Monday, given the cooler air being advected
into the region.

Outlook...

Mon-Tue...Dry weather with VFR conditions except perhaps some AM
valley fog N.

Wed...PM TSRA moving across from W-E.

Thu...A chance of showers and storms.

&&

.HYDROLOGY...
Over half of an inch of rain last night and this morning over
the far NW has increased confidence that the precip in the N
will be very efficient today. While dbZ and the amt of ltg may
not impress today, the moist adibatic profiles and deep warm
layer will make for heavy rain at times. Draw back to fast storm
motions: 1) radar may underestimate precip as the fast cells
skip along in between scans, and 2) it`s tough to get flooding
when the cells have a low residence time. However the repeated
showers/storms could (easily) overcome that issue.

Prev...
The area of greatest concern for heavy rain and flash flooding
will spread south and east later this morning through this
afternoon as the axis of the LLJ slides east and the favorable
RR quad of an approx 2 sigma upper level jet and its enhanced
MESO-B lift moves overhead.

PWAT values increased steadily from west to east overnight from
a little over one inch to start the night to around 1.6 inches
early today.

PWATS via the GEFS will peak around +3 sigma or about 2.25
inches later this morning through this afternoon (which are
values that haven`t been seen so far in PA during 2024). This
anomalous, deep moisture will support the threat for locally
very heavy rain (in excess of 2 inches/hour) within a broad
area of 1 to 1.5 inch basin average storm total rain forecast
for much of Central and Northern PA. Issued a Flood Watch from
12Z today through 06Z Sunday for much of Central and Northern
PA where FFG values are well under 2 inches/3 hours across
parts of the Northern Mtns.

&&

.CLIMATE...
Through 6/27, June ranks as the second warmest on record at
Harrisburg with an average monthly temperature of 76 degrees or
+3.8 degrees above normal.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Lambert/DeVoir/Fitzgerald
NEAR TERM...Lambert/DeVoir/Fitzgerald/Dangelo/Martin
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald/Bauco
AVIATION...Martin
HYDROLOGY...Lambert/Dangelo
CLIMATE...Steinbugl